Where do you see your tracker defined at ECB +0.75%? Looked in my contract but not defined in part 1
Where you ever on a tracker? If so, it will clearly outline the margin. Don't have the docs with me now, so can't say what page/section, but it's the section that describes the details of the loan (rate, amount, duration etc)
If you were never on a tracker, then it may be difficult to specify the exact margin you should be on. but you should definitely try and find out what margin was applicable at the time you took out the loan.